This invention relates to new synthetic compounds of the penicillin and cephalospor in classes which are useful as antibacterial agents. These compounds possess a high degree of activity against a large number of microorganisms, particularly penicillinase-producing micro-organisms. As antibacterial agents the compounds of this invention are therapeutically effective in the treatment of infectious diseases due to gram-positive and gram-negative bacteria in poultry and animals, including man. In addition, the compounds of this invention are useful as animal feed supplements and as the active ingredient in germicidal preparations employed as surface disinfectants.